Routine String Trimmer Maintenance

The string trimmer has a vital role in maintaining one's yard. It can trim those out-of-the-way spots your lawn mower can't reach. This, coupled with the ease and versatility provided by a variety of attachments, makes the string trimmer an indispensable hand tool to have hanging on your garage wall. Let's make sure it is ready to perform with some easy-to-follow maintenance tips.

The most important tip we can provide is to always refer to the owner's manual that came with your string trimmer - we recommend keeping it available over the lifetime of your product. In addition to the valuable safety and operating instructions, every owner's manual comes with a table which outlines a suggested maintenance schedule. If you do not have your owner's manual, you can download one from our model finder with a model and serial number.

For the purpose of brevity, we will avoid the general topic of replacing the trimmer line. There are a few different string trimmer heads - some wind single lines, some wind dual lines, and others have hooks for pre-cut lengths. Please refer to your owner's manual if you have any questions about refilling the trimmer line for your particular model.

Inspect the cutting shield for damage or a build-up of debris. Also, inspect the gear box to ensure it is free of debris such as long grass, string, or anything that would prevent the trimmer head from turning freely. Before inspecting these parts, confirm that your machine has stopped running and all moving parts have stopped spinning. As an added measure of safety, remove the spark plug wire from the spark plug before you do any maintenance on your product.

Inspect the Air Filter

Cleaning and re-oiling the string trimmer air filter is necessary maintenance. A clean air filter improves performance and prevents engine damage. The steps for this include:

Make sure the engine is off and cool to the touch.
Open the filter cover and remove the air filter.
Replace the filter with a new one if necessary. If reusing the existing air filter, wash the filter with detergent and water. Rinse the filter and let it dry.
Lightly coat the filter with clean SAE 30 oil to keep debris from getting sucked into the engine. Squeeze the air filter to distribute the oil, and to remove any excess.
Re-install the filter in the trimmer and close the filter cover.

Inspect the Spark Plug

Replacing the string trimmer spark plug is another regular maintenance activity you will want to perform.

Make sure the engine is off and cool to the touch.
Remove the spark plug boot.
Remove the spark plug with a 5/8 socket. Check the spark plug to see if it is fouled, blackened, corroded, or damaged.
If needed, replace the spark plug with the model specified for your trimmer. You will find this information in your owner's manual.
Use a feeler gauge to set the gap according to your owner's manual.
Re-install the spark plug and tighten by turning the 5/8 socket clockwise until snug. Do not overtighten the spark plug.
Put the spark plug boot back onto the spark plug.

Check the Oil Level (4-cycle engines)

If you own a string trimmer with a 4-cycle engine, you do not have to combine the fuel and oil as required for 2-cycle engines. However, you do need to check the oil level before every usage. The importance of this step cannot be overemphasized. It is very important to maintain the correct level of oil in your equipment. In order to do this:

Make sure the engine is off and cool to the touch.
Set the string trimmer on a flat, level surface such as a workbench or table. The cutting head should hang over the edge so that the engine is level.
Check the oil level. How to check the oil level is specific to your model. Some models have a dipstick attached to the oil fill plug. Some models have an oil level window.
If the oil level is too low, you will need to add oil to the correct level. Do not overfill the reservoir.

We recommend that you change the oil - again, specific to owners of string trimmers with 4-cycle engines - after the first 10 hours of use and every 28 hours thereafter. Changing the oil requires the following:

Make sure the engine is off. However, you will want to change the oil while the engine is still warm. This allows the oil to flow freely and carry away more of the impurities that have built up over time.
Clean the area around the oil fill plug to prevent debris from entering the oil fill hole.
Unscrew the oil fill plug.
Tip the unit vertically to pour the oil out of the oil fill hole and into a container. Allow sufficient time for complete drainage.
Wipe up any oil that may have spilled.
Pour new oil into the oil fill hole.
Wipe up any oil that may have spilled.
Re-install the oil fill plug.

Note: Dispose of the old oil according to federal, state, and local regulations.

Proper maintenance will keep your string trimmer humming throughout the season and help you maintain an immaculate yard.

Find Maintenance Parts Quickly

When you need parts for your string trimmer, you can use the MTD Genuine Parts Part Finder to find the correct one. Common parts include:

Shop Equipment and Parts

The MTD Genuine Parts Knowledge Center provides do-it-yourself instructions for performing many basic maintenance items, including replacing cutting blades, drive and deck belts, and engine oil. If you find your machine has a bigger problem, use our service locator to find a qualified MTD service provider in your area.